As discussed in (for example) U.S. Pat. No. 5,031,618 to Mullett, U.S. Pat. No. 7,313,440 to Miesel, and U.S. Patent Appln. Pub. 2010/00010381 to Skelton et al., implantable stimulators are sometimes used to deliver electrical stimulation to the spinal cord (or other tissue) of a patient via one or more implantable leads, typically to alleviate pain or provide other therapeutic effects. An exemplary arrangement of this nature is depicted in the accompanying FIG. 1, wherein an implantable stimulator 100 is shown implanted within a patient's body with a pair of leads 102 extending from the stimulator adjacent the spinal column. The leads bear electrodes (not shown) spaced along their surfaces through which stimulation is delivered to the spinal cord. The delivered stimulation can generate a tingling sensation that tends to mask, or sometimes entirely eliminate, the patient's pain.
As the foregoing references note, it can be desirable to vary stimulation parameters (e.g., pulse amplitude, pulse width, and/or pulse frequency) depending on the patient's body orientation; for example, a patient using an implantable spinal neurostimulator for chronic pain relief may require less stimulation when standing up than when the patient is recumbent. An input device 104 can be used by the patient, or by medical personnel, to adjust the stimulation parameters. Alternatively or additionally, a stimulator may incorporate an accelerometer or other orientation sensor which automatically adjusts stimulation based on the orientation of the sensor (which tends to indicate the patient's posture), and possibly based on motion of the sensor as well, e.g., how long the patient remains in a particular orientation.
While automatic adjustment of stimulation based on patient orientation and activity is useful, it can sometimes fail to adequately adjust stimulation. For example, such stimulation adjustment techniques may provide the same stimulation when a patient is standing and facing forwardly, and when the patient is seated upright but with his/her head, shoulders, and torso turned to look rearwardly. In this case the patient's detected orientation is the same, but his/her actual body positioning is very different, and certain patients may need different stimulation for such different body positions. It would therefore be useful to have further stimulation adjustment schemes which improve on conventional methods.